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Search: id:A163193
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| A163193 |
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Positions n such that sigma(n)= 2*sigma(n+1). |
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+0
1
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| 12, 70, 88, 204, 220, 1750, 1888, 2958, 8142, 8632, 9114, 14664, 18414, 18762, 20118, 20712, 25194, 45520, 64206, 65652, 65964, 77814, 79338, 79824, 85096, 90804, 103410, 103644, 117822, 158946, 163938, 176364, 185776, 186612, 194416, 202656
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OFFSET
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1,1
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COMMENT
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The cases sigma(n)=3*sigma(n+1) are rarer: n=180, 12000, 30996, 47940,... [R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 25 2009]
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FORMULA
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{n: A000203(n)= 2*A000203(n+1)}.
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MATHEMATICA
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f[n_]:=DivisorSigma[1, n]; lst={}; Do[If[f[n]==f[n+1]*2, AppendTo[lst, n]], {n, 9!}]; lst
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CROSSREFS
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Cf. A067081, A002961, A058073.
Sequence in context: A096425 A101097 A067702 this_sequence A088832 A060930 A101523
Adjacent sequences: A163190 A163191 A163192 this_sequence A163194 A163195 A163196
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KEYWORD
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nonn
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Jul 22 2009
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EXTENSIONS
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Edited by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 25 2009
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